As alluded to in prior art drawing FIGS. 1A, 1B, and 1C, robbery alarm switches employable by a cashiering accostee and capable of actuating a summoning alarm oftentimes include a reedswitch internal component. In a general sense, a typical such robbery alarm switch (having a reedswitch component) is taught, intera lia, by U.S. Pat. No. 3,418,611 (Pounds--12/14/1968). A basic reedswitch (e.g. 10A) customarily comprises a pair of substantially longitudinally colinear (10) and magnetically-permeable reeds (11, 12) mounted at a finite-gap G by a surrounding magnetically-impermeable envelope (e.g. glass envelope 10E). Whenever a source of magnetic flux (e.g. permanent magnet 30A, 19) and having appropriate directional orientation of its magnetic polarities (N, S) is brought alongside the reedswitch, the reeds (11, 12) become of opposite magnetic polarities whereby the normal finite-gap (G) is extinguished. Accordingly, an external voltage potential (V) might provide an amperage flow through the reedswitch reeds (11, 12).
In prior art drawing FIGS. 1A, 1B, and 1C, "C" generally refers to an occupiable cashiering locale having a windowed (W) partition "P" intervening between a cashiering person and visitors to his/her cashiering locale. Because a would-be robber might be among such visitors, locale "C" usually has a partition attached alarm (e.g. bell "K") and electrical voltage (V), plus an intervening robbery alarm switch (SA, SB, SC) equipped with a single manual actuator (e.g. a plunger 20A). Thus, if a would-be robber accosts the cashier, he/she can depress this lone plunger (20A) to actuate alarm K for summoning police or other security personnel.
Each of the prior art robbery alarm switches (SA, SB, SC) has a rectangular housing 100 attachable to the environment (e.g. at partition "P") and including a base-panel 101 and a parallel cover-panel (herein removed for clarity). Interposed between the housing base-panel and cover-panel are: a left-panel 104, apertured right-panel 105, a bottom-panel 103, and apertured top-panel 102. Conventionally adherently or otherwise attached to base-panel 101 is a reedswitch (10A, 10B, 10C, etc.) An electrically conductive terminal (e.g. wire Y2) extends between reedswitch reed 12 (and via voltage V) and one terminus of alarm K. In the alarm switches SA and SB, another terminal (e.g. wire Y1) extends from reedswitch reed 11 toward the other terminus of alarm K. Spindle 23 of lone plunger member 20A extends through said apertured right-panel 105. Within housing 100, plunger spindle 23 carries a permanent magnet (30A) source of magnetic flux. Magnet 30A extends parallel to reedswitch axis 10 whereby its North-South (i.e. N-S) magnetic polarity is termined as "relatively longitudinal". Externally of of housing 100, plunger spindle 23 carries a manually engageable pushbutton 21. For this lone or "alpha" plunger member 20A, a helical spring 24 surrounds spindle 23 between right-panel 105 and pushbutton 21. Thus, alpha-plunger 20A has a normal first-station wherein the non-housed pushbutton part (21) is located relatively remote from the housing and wherein its housed magnet addendum (30A) is located sufficiently remote from the reedswitch so as to not influence the distance between the reedswitch reeds 11 and 12. However, and as aptly indicated in the phantom lines, when pushbutton part 21 is manually depressed toward housing panel 105, plunger 20A assumes a second-station wherein its housed magnet addendum (30A) is located relatively nearer to the reedswitch and effects a change in the distance between the reed-switch reeds (11, 12).
For robbery alarm switch SA of FIG. 1A, the housed reed-switch is elementary and non-supplemented by a co-stationed biasing-magnet (e.g. 19); hence, it is termed a "normally-open" reedswitch 10A i.e. having gap "G" between reeds 11 and 12 when plunger 20A is at normal first-station. However, when plunger 20A is manually depressed to its second-station, magnet addendum 30A there sufficiently magnetically attracts reeds 11 and 12 whereby gap "G" is extinguished and electrical current might flow between the reeds to actuate alarm K.
On the other hand, robbery alarm switch SB of FIG. 1B uses an elementary reedswitch co-supplemented by a biasing-magnet (e.g. 19), and hence, is termed a "normally-closed" reedswitch 10B. Appropriate in this regard, a conventional relay "R" (and typically comprising coil and resiliently pivoted contacts) is interposed between voltage "V" and wire Y1. Accordingly, when plunger 20A is manually depressed to its second-station, addendum magnet 30A, which has a polarity orientation opposite to that for biasing-magnet 19, magnetically neutralizes biasing-magnet 19 whereby gap "G" is re-established and electrical current might flow between the reeds to actuate alarm K.
FIG. 1C illustrates another "normally-closed" switch SC that utilizes a single-pole double-throw type reedswitch 10C. Such prior art reedswitch 10C differes primarily from elementary reedswitches 10A and 10B in that envelope 10E tends to ensure that a third and magnetically-impermeable reed 13 normally touches reed 12 but is spatially offset from reed 11. Accordingly, when plunger 20A is manually depressed to its second-station, magnet addendum 30A sufficiently attracts magnetically-permeable reeds 11 and 12 whereby gap "G" is extinguished and electrical current flows therebetween to actuate alarm K.
Admittedly, the prior art robbery alarm switches alluded to in the aforedescribed drawing FIGS. 1A, 1B, and 1C, will reliably actuate a summoning alarm (K) whenever a cashiering person causes depressible movement of the plunger activator (20A). Unfortunately, there is the likely possibility that a busy cashiering person might inadvertently bump into such sole activator (e.g. 20A) and accidentially actuate the summoning alarm to a "false alarm" status. Such inadvertent "false alarm" is not only embarrassing to the cashier, but also represents a costly waste of the needlessly responding police or other summoned security personnel.